Garlic Mustard Monitoring Protocol

June 2003
Ecology and Management of Invasive Plants Program
122E Fernow Hall, Cornell University, Ithaca, New York 14853 USA
homepage: http://www.invasiveplants.net
with
Victoria Nuzzo, Natural Area Consultants
1 West Hill School Road, Richford, New York 13835 USA
vnuzzo@earthlink.net 607-657-8611

Introduction:

Garlic mustard (Alliaria
petiolata) is a biennial European herb that invades
forested communities in North America, especially in the central and
eastern part of the US and adjacent Canada. A biological control
program targeting garlic mustard was initiated in 1997. Four
weevils (Ceutorhynchusspp)
including two stem-feeders, a seed-feeder, and a root-crown feeder,
are under study, and releases of the first insects are anticipated
to begin in 2004-05. The following guidelines are intended to help
monitor the abundance of both garlic mustard and the
biocontrol
insects, and assess the long-term impact of biological control. The
protocol can also be used to detect change in herbaceous vegetation
relative to change in garlic mustard. For maximum information,
monitoring should ideally be initiated one or more years before
biocontrol
organisms are released: the resultant ‘pre-release’ data will
provide a baseline to assess ‘post-release’ changes. For best
results, monitoring should be conducted twice a year; in June to
assess garlic mustard density and seed production, and in October to
assess rosette abundance and external evidence of insect feeding.

Garlic mustard is an obligate biennial and can only spread by seeds;
therefore the goal of biocontrol is
population reduction, achieved by reducing total seed production.
Garlic mustard seeds germinate in early spring, and form a basal
rosette by June. Plants remain as rosettes through the winter, and
produce flower stalks the following spring, usually blooming in
April - May, depending on the location and temperature regime.
Seeds are produced in siliques (linear pods) 4-8 weeks later, usually in
June-July. Garlic mustard seeds live >5 years in the seedbank.

The four weevils are difficult to observe directly. Larvae induce
most of the damage, but because they feed inside the plant (in
seeds, stems, leaves, and root crowns) they are not usually
observed. Adults are small (2mm) and black, and feed on stems and
petioles, leaving a ‘scraping’ mark. In addition, all four weevils
produce a characteristic ‘window pane’ feeding pattern that can be
easily observed on the leaves. Under heavy attack by one or more of
the weevil species, garlic mustard plants become shorter and less
robust, often have tip dieback, and produce fewer flowers and
siliques.

Site Selection and Quadrat Setup:

Select a monitoring site that will be protected from other uses that
may jeopardize your continued monitoring. It is imperative that the
monitoring site be protected from all management that could damage
the insects or the garlic mustard plants, in particular burning,
herbicide application, and pulling of plants. We do not know how
the weevils will respond to fire or flooding, and in the initial
establishment phase a fire (which may burn the insects), flooding
(which may drown the insects), or removal of garlic mustard plants
(with the insect larvae hidden inside) could eradicate small
populations. The study site should be sufficiently distant from a
trail to limit vandalism.

The study site should contain a well-established garlic mustard
population (> 0.5 ha). Garlic mustard does not need to form
a continuous carpet, but should be present throughout the study area
every year, as rosettes and/or adult plants. To determine response
of the associated groundlayer vegetation
to the anticipated reduction in garlic mustard, it would be
beneficial to locate the study site in an area with native
vegetation. Avoid establishing plots in a site where garlic mustard
has been present for <3 years, as the population should be large
enough with a well-established seed bank to maintain a reliable food
source for the weevils.

We recommend an open-ended quadrat
frame with the fourth side removable. Construct the
quadrat
frame from a 10' length of 1/2" diameter PVC or CPVC pipe, 4
right-angle elbows of the same diameter, and PVC or CPVC glue.
The inside dimensions of the finished frame should measure 1m by
0.5m. After cutting the conduit to the correct lengths, glue
two elbows to each 1m long piece (make sure the elbows are
perfectly aligned to each other). Set one piece aside (This
will be the fourth side of the frame). Glue the elbows of the
other 1m long piece to two 0.5m long pieces to form the open ‘u’
shaped frame. Using a permanent marker, mark 1 dm intervals on
each side to assist with estimating percent cover. In the
field,

slide the open-ended U-shaped frame along
the ground to avoid disturbing the vegetation. Then, attach the
fourth side to the frame.

We recommend a total of 20 permanent 0.5m2 (0.5m x 1.0m)
quadrats, spaced >10 meters apart. This allows
statistical analysis of the expected decline in garlic mustard, and
provides sufficient locations to ensure that garlic mustard is
present as adult or seedling in most quadrats
each year (in general, once garlic mustard is present, it will
continue to be present almost every successive year in that
location, although densities may vary significantly).

Quadrats can be located in several ways:
along two parallel transects, in 4 rows of 5
quadrats, or completely randomly. Relocating the
quadrats
is easier using parallel transects, and this method will be outlined
here. Randomly establish two parallel transects, at least 100m long
and >10 meters apart. Locate quadrats
at fixed intervals >10 meters apart along each transect.
ALL quadrats must contain garlic mustard; if necessary, shift the location of the
quadrat
so that garlic mustard covers at least 25% of the
quadrat. In sites where both age classes (adults and
rosettes) are present, makes sure that these age classes are
represented in the 20 quadrats. Record
the position and numbers of quadrats on
the vegetation map on Form 1. Use GPS coordinates for easy
relocation in dense vegetation. Locate permanent photo-points and
take photographs of study site, including one or more
quadrats.

To establish the permanent quadrats, first
locate the position of each quadrat, then
place the quadrat frame on the ground, and
mark the four corners by driving a 30-50cm long and 1/2" diameter
plastic or aluminum conduit into the ground. This will allow exact
placement of the quadrat in future years. Write the quadrat number on each conduit with a permanent marker or
other means. In areas with high public use and potential vandalism,
conduits should be short and difficult to see. Obvious markings can
attract vandalism and ‘helpful protectors’ who remove the conduits.
Avoid trampling vegetation in and near the
quadrat.

Data Collection

Assessment of the plants and insects will occur twice each growing
season. Four data forms are provided and described in detail on the
following pages: Site location (Form 1); Summer monitoring (Forms 2a
and 2b), and Fall monitoring (Form 3). In addition, ‘Quick
Reference’ sheets are provided to use in the field. To assess the
growth and abundance of garlic mustard, and growth of other
groundlayer species, a series of estimates are used. All
estimates reflect the growth within each quadrat
and NOT of the site as a whole, or plants near but not in the
quadrat.

Form 1: Site location, background information

Site Location:

Enter name of the site (for example:
Fillmore
Glen
State Park, north unit: be as specific
as possible); and the location (town, county, state, etc.). If
Global Positioning System (GPS) coordinates are available, enter
this information in the spaces provided.

Contact Person and Legal Landowner:

Provide the name, address, telephone number and email address of a
contact person. This person can be the releaser or a local
contact. If the contact person is not the legal landowner, please
provide this information in addition.

Site Characteristics:

Check one of the options or provide specifics if none of
the options are applicable.

Road Map:

Photocopy a road map (preferably a county road map) to the site from
a Road Atlas or MapQuest and paste it into
the space provided. Mark the location of the site. An arrow should
indicate North on the map. If a written description of directions
is needed, attach the description to this page. Be specific: assume
the reader has never been to the locale. Attach additional pages if
needed.

Site and Vegetation Map:

Provide a map of the area, or copy of an aerial photo, with access
roads, approximation of garlic mustard infestation outlined, other vegetation types, trails, creek etc. An arrow
should indicate North on the map. Paste map into space provided.
Once insects are available for release, indicate with Arabic
numerals (corresponding to numbers under Insect Release) points of
single or multiple control agent releases

Photographs of changes in vegetation over time are a powerful tool
for presentations or to re-enforce quantitative data. One or
several permanent photo-points should be marked in the monitoring
area using flagging tape or stakes driven into the ground. The
position of these photo-points should be indicated on the vegetation
map, and the direction in which the picture was taken should also be
indicated with an arrow. Take pictures once a year at the same time
of the year. The showy flowers of garlic mustard suggest taking
pictures at the peak of the flowering period. Make sure to record
which photos were taken from which location and when.

Insect Release History:

Document date, control agent species, life stage (adults, eggs or
larvae), the number of individuals released, how individuals were
released, time of day and weather conditions. Code each release with
an Arabic numeral and insert number at the release point on the
vegetation map (see above).

Summer data should be recorded when garlic mustard has completed
flowering and has fully formed green siliques,
but before the siliques turn brown and
start to disperse seed. In northern locales this is usually in
mid
to late June, while in southern locales this may be as early as mid
May. Begin with quadrat 1 and fill out
both Form 2a, and then Form 2b (if adult garlic mustard are
present), then move to the next quadrat. Use new data sheets each year. Summer monitoring
is easier with two people, one to make the observations and the
other to record data.

1) Before collecting data, please record in spaces
provided: site name, date (year, month, day), and the names of the
observers (last name, first name), as well as general weather
pattern (sunny, overcast, rainy, humid), temperature, and time of
day of observations. Take photographs at permanent photo points.

2) First, slide the frame into position. Standing over
the frame, and looking straight down, estimate how much of the
quadrat is covered by garlic mustard and, independently, how
much is covered by all other vegetation (Use cover estimates in
Chart A, or a finer scale (for example. Present;
<1% cover; 2-5% cover, and in 10% increments thereafter i.e.;
>5-15%, >15-25%, etc). If both garlic mustard and other
vegetation are abundant, these estimates may total >100%, due to
layering. Next, focus only on garlic mustard. If adult garlic
mustard plants are uncommon or small, or if only seedlings are
present, you may need to carefully move vegetation to determine how
much garlic mustard is actually present in each age class. Estimate
the actual percent cover (using the cover classes in Chart A) of all
garlic mustard; of only adult garlic mustard; and of only seedling
garlic mustard. Often, adult garlic mustard will overtop seedling
garlic mustard, and their combined cover will therefore exceed the
‘all garlic mustard’ cover. That is okey,
as we are interested in monitoring how much of each size class is
present.

3) Next, scan the garlic mustard for any damage to the
leaves, shoots, or siliques. After insect
release, look especially for the ‘window pane’ feeding pattern of
the biocontrol weevils. Some windowpane
feeding is already present but in ---- This
may originate from native species or accidental introductions.
Estimate the percent leaf area of garlic mustard removed by insect
feeding integrated over the entire quadrat,
using Chart A. Initially, this will be very low or non-existent.
After weevil populations build up you may find as much as 50% of the
leaves are damaged. Next, indicate what type of damage is visible,
such as leaf miners, deer browse, disease, etc., using a ‘check’ or
‘+’ in the appropriate box. This may be omitted if feeding damage
is very low (<1%) and not clearly discernible. Make a note if some
other type of damage is present, and include a sketch or photograph
of the damage.

Estimating the amount of leaf area removed by insect feeding will
initially be difficult because you need to scan through the
vegetation, and leaves and plants will show different amounts of
feeding damage, but you will get better over time. Experienced
observers should introduce new personnel to the methods and to their
assessments to increase the accuracy of reported results. We expect
to observe large differences over time, especially following high
abundance of Ceutorhynchus
larvae and adults.

4) Count the number of seedlings. If seedling density is
very high, count the number of seedlings in a section of the
quadrat, and then use this density to estimate the total
number of seedlings in the quadrat. If time does not allow counting individuals or a
subset of the population, use Chart B to estimate seedling density.
Estimations are never as accurate or powerful as actual counts, so
count actual seedling density whenever possible.

5) Looking below
all vegetation, estimate the cover of soil, wood, leaves and rock
using Chart A or actual percent cover: This should total 100%.
Often, sites with abundant garlic mustard have little leaf litter.

6) Measure litter depth to the closest cm in the center
of each half-quadrat.

7) If you are interested in monitoring the associated
groundlayer vegetation, record presence (and estimated
percent cover) of all species rooted in the
quadrat. Use cover estimates in chart A, or a finer scale
(for example. Present; <1% cover; 2-5% cover, and
in 10% increments thereafter i.e.; >5-15%, >15-25%, etc).

8) Other Observations: Record any general observations
or useful information about the site; windfall, flooding, deer
herbivory, insects etc. Most of this information will be
difficult to evaluate, so do not spend too much time on this.

Instructions for Form 2b: Garlic Mustard
Biocontrol
Monitoring (Adult height and number siliques)

Use this form when adult garlic mustard are
present in the quadrat. Write the quadrat number in the appropriate box at the top of the
sheet. Then, beginning at one corner of the
quadrat
and working systematically across the quadrat,
measure the height in cm, and count the number of
siliques, of each garlic mustard stem. Record this
information in the appropriate boxes below the
quadrat number. Record each stem that originates from the
ground as a separate stem, even if you suspect that some stems may
originate from a single root. When a stem branches >2cm above the
ground, then the branch is counted as part of the single stem.
Also, look carefully for short, frequently sterile stems. These
small plants are usually overlooked, but it is important to record
their presence. Record every stem, using several columns if
necessary, and writing the quadrat number
above each column. To be counted, a stem must originate within the
quadrat; if it originates under the frame, then it is not
recorded.

If you see overt damage or anything unusual on a stem, you can
record this in the same box, by using an asterix,
or a letter, or other symbol, and defining it in the box labeled
“notes”. For example, if you see leaf mining on a stem 30cm tall
with 7 siliques, you could record this by writing “30-7 *” on the
data sheet and writing in the notes box “ * = leaf mining”.

It is important to measure every stem in the quadrat, even if some quadrats
have numerous plants. We anticipate that under heavy insect attack
garlic mustard plants will decrease in density, height, and
silique
production, and will also change in plant architecture and produce
more small side branches. Therefore it is very critical to have
accurate baseline data to compare to ‘post-release’ data, and
accurately assess the impact of the weevils on garlic mustard.

Instructions for Form 3: Garlic Mustard
Biocontrol
Monitoring (Fall)

These are similar measures to those collected in summer, except that
flower stem density and height are not measured. Because only one
size class (rosette) is present, the autumn monitoring takes less
time than the spring monitoring, and can be conducted by one
individual. Monitoring should occur about the time deciduous trees
lose their leaves. Indicate in the ‘notes’ box whether trees have
lost some, all, or none of their leaves (this helps with
interpretation of leaf litter depth, and of garlic mustard percent
cover, as small rosettes are often covered by new leaves and will be
missed in sampling).

1) First, if insects have been released, approach the
quadrat slowly and observe for weevils. Typically, only the
rosette-feeder C. scrobicollis
will be active at this time. You may see these small (2 mm) black
insects near the center of a rosette.

2) Next, slide the frame into position. If insects have
been released, count number of weevils observed in one minute. As
long as you are able to count the exact number of weevils, please
provide that number. If the allowed search time does not enable you
to count all present individuals, use estimates in Chart B.
Standing over the frame, and looking straight down, estimate how
much of the quadrat is covered by garlic
mustard and, independently, how much is covered by all other
vegetation (Use cover estimates in Chart A, or a finer scale (for
example. Present; <1% cover; 2-5% cover, and in
10% increments thereafter i.e.; >5-15%, >15-25%, etc). If
rosettes are uncommon or small, or tall vegetation is present, you
may need to carefully move vegetation to determine how much garlic
mustard is actually present. If both garlic mustard and other
vegetation are abundant, these estimates may total >100%, due to
layering. That is okey, as we are
interested in monitoring how much of each is present.

3) Next, scan the garlic mustard for any damage to the
leaves, shoots, or siliques. After insect
release, look especially for the ‘window pane’ feeding pattern of
the biocontrol weevils. Some window pane
feeding is already present but in low abundance. Autumn is when
this feeding pattern is most distinct if the
rootcrown feeder C. scrobicollisis present. Estimate the percent leaf area
of garlic mustard removed by insect feeding integrated over the
entire quadrat, using Chart A. Initially,
this will be very low or non-existent. After weevil populations
build up you may find as much as 50% of the leaves are damaged.
Next, indicate what type of damage is visible, such as slugs (round
holes >1 cm diameter), deer browse, disease, leaf miners, etc.
using a ‘check’ or ‘+’ in the appropriate box. This may be
omitted if feeding damage is very low (<1%) and not clearly
discernible. Make a note if some other type of damage is present,
and include a sketch or photograph of the damage.

Estimating the amount of leaf area removed by insect
feeding will initially be difficult because you need to scan through
the vegetation, and leaves and plants will show different amounts of
feeding damage, but you will get better over time. Experienced
observers should introduce new personnel to the methods and to their
assessments to increase the accuracy of reported results. We expect
to observe large differences over time, especially following high
abundance of Ceutorhynchus
larvae and adults

4) Count the number of rosettes. If rosette density is
very high, count the number of rosettes in a section of the
quadrat, and then use this density to estimate the total
number of rosettes in the quadrat. If
time does not allow counting individuals or a subset of the
population, use Chart B to estimate rosette density. Estimations
are never as accurate or powerful as actual counts, so count actual
rosette density whenever possible.

5) Looking below all vegetation, estimate the cover of
soil, wood, leaves and rock using Chart A. This should total 100%.
Often, sites with abundant garlic mustard have little leaf litter.

6) Measure litter depth to the closest cm in the center of
each half-quadrat.

7) If you are interested in monitoring the associated
groundlayer vegetation, record presence (and estimated
percent cover) of all species rooted in the
quadrat. Use cover estimates in chart A, or a finer scale
(for example. Present; <1% cover; 2-5% cover, and
in 10% increments thereafter i.e.; >5-15%, >15-25%, etc).

8) Other Observations: Record any general
observations or useful information about the site; windfall,
flooding, deer
herbivory, insects etc. Most of this information will be
difficult to evaluate, so do not spend too much time on this.